The present invention relates to a system for controlling a plurality of units by transferring serial data from a computer. More particularly, the invention is directed to a control system suitable for controlling a display system consisting of a plurality of display units, e.g., projection TVs.
In the following, two conventional communication networks are described in which a plurality of units, e.g., display units U1-U4 using projection TVs, are controlled by transmitting serial data from a computer.
As shown in FIG. 7, a first example is such that a single distributor 7 is interposed between a computer 1 and each of display units U1-U4, and that transmission data from the computer 1 is selectively distributed to either one of the display units U1-U4 by the distributor 7. The selection among the display units U1-U4 involves the process that the distributor 7 decodes an identification code (hereinafter referred to as "ID code") included in the transmission data, which code serves to identify one of the display units U1-U4. Data succeeding the ID code is thereafter taken by, e.g., the display unit U1, which then adjusts the luminance or color of an image as instructed by the data.
As shown in FIG. 8, a second example is such that a computer 1 is connected to each of display units U1-U4 via a bus 8. Specific ID codes are preassigned to the respective display units U1-U4, and an ID code included in transmission data from the computer 1 is decoded by each display unit. If the ID code indicates that the transmission data is directed to, e.g., the display unit U1, the display unit U1 takes in the transmission data. In this example, each of the display units U1-U4 must be provided with setting switches and a memory such as a ROM for setting and storing its own ID code, respectively.
According to the first example (FIG. 7), a network must include the distributor 7 to select from among the display units U1-U4, thus increasing the number of components. From the viewpoint of system expandability, the number of display units distributable by a single distributor 7 is limited, so that additional distributors may have to be provided to increase the number of display units. This makes it difficult to expand a system. Recently, a wide-area display system was developed using a total of 108 display units (a matrix of 9.times.12). There is some difficulty in transmitting serial data in a system which includes such a large number of display units.
According to the second example (FIG. 8), each of the display units U1-U4 must be provided with hardware such as setting switches for setting an ID code and a ROM for storing the same, again unavoidably increasing the number of components. In addition, because of the system construction employing a bus, a signal attenuates as it goes farther away from the computer 1. This means that there exists a limit of the signal line length, which further imposes a certain limit on display unit expandability. Moreover, with respect to the assignment of specific ID codes to respective display units, if additional display units are to be provided, more specifically, if a large screen is to be implemented by combining display units in a matrix form, ID codes may have to be reassigned or changed over the entire network, depending on the installation position of the additional display units. In such a case, a cumbersome operation of reassigning the ID codes of the respective display units must be performed.